The efficiency ($\eta$) of a transformer is defined as the ratio of output power ($P_{out}$) to input power ($P_{in}$). Formula: $\eta = \frac{P_{out}}{P_{in}} = \frac{V_s I_s}{V_p I_p}$ . Given: Input Voltage ($V_p$) = 220 V Output Voltage ($V_s$) = 440 V Output Current ($I_s$) = 2.0 A Efficiency ($\eta$) = 80% = 0.8

Calculation:

1. Calculate Output Power: $P_{out} = V_s I_s = 440 \text{ V} \times 2.0 \text{ A} = 880 \text{ W}$.
2. Calculate Input Power: $P_{in} = \frac{P_{out}}{\eta} = \frac{880}{0.8} = 1100 \text{ W}$.
3. Calculate Primary Current: Since $P_{in} = V_p I_p$, then $I_p = \frac{P_{in}}{V_p} = \frac{1100}{220} = 5.0 \text{ A}$.